The 61-year-old Harwell Dekatron — about the size and weight of an SUV — was originally hailed as a slow, steady machine capable of delivering error-free calculations while running for 90 hours a week. It has survived to become the oldest original working digital computer following the announcement of its completed restoration by The National Museum of Computing in the U.K. on Tuesday.

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The computer relies on 480 relays that have more in common with telephone exchanges rather than modern PCs or Macs. Such relays sit inside a collection of racks that also hold 828 flashing Dekatron valves — gas-filled counting tubes used in the early days of computing rather than the transistors of modern electronics.